Calibration purpose

Dead-weight gauges (used for calibration purposes only)... 

For control or calibration purposes, film thickness can be determined by mounting a sectioned specimen and measuring the oxide film thickness directly on the screen of a projection microscope at a known magnification. Alternatively, the loss in weight of an anodised sample of known area may be found after the film has been stripped in a boiling solution made up as follows ... 

Prepare the buffer solutions for calibration of the pH meter if these are not already available the potassium hydrogenphthalate buffer (pH 4), and the sodium tetraborate buffer (pH 9.2) are the most commonly used for calibration purposes. 

For further discussion and for calibration purposes we will have to define a reference solution reaction which would be sufficiently related to the given enzymatic reaction. This will help us in removing the problems associated with concentration effect and in focusing on the actual catalytic advantage of the enzyme. To do this we describe the reference reaction in solution as... 

Kragten, J., Least-Squares Polynomial Curve-Fitting for Calibration Purposes (STATCAL-CALIBRA), Ana/yrica Chimica Acta 241, 1990, 1-13. 

There are two main uses of a RM calibration and method performance checking. ISO Guide 32 (1997) deals with the use of RMs for calibration purposes. RMs used for calibration purposes are usually RMs prepared by synthetic means. Commonly, the property values of these RMs are known from preparation, and verified by some kind of suitable measurement technique. This can be a technique directly providing a value for a property of interest, or a technique that allows the comparison of the new material against older measurement standards. 

ISO Guide 32 provides guidance in two ways. Apart from the guidance on using RMs for calibration purposes, it also provides information on the preparation and use of calibrants in a laboratory, and checking them against other RMs or measurement standards. 

Some of the intended categories of use of radioisotopic reference material have been reviewed recently by Fajgelj et al. (1999). They include assignment of property values, establishing the traceability of a measurement result, determining the uncertainty of a measurement result, calibration of an apparatus, assessment of a measurement method, use for recovery studies and use for quality control purposes. It should be noted however that, in general, natural matrix reference materials are not recommended for calibration purposes. This should preferably be done with pure chemical forms of the element labelled with the isotope of interest. Calibrated isotopic sources of this kind are available from a number of commercial suppliers and are not the subject of this review. 

The concept of preparing a reference material with property values traceable to SI units is a relatively recent one which has not yet been applied in practice to natural matrix radioisotopic reference materials. This is one of the main reasons why such materials are generally not recommended for calibration purposes. 

A significant change in geochemical analysis, and in the demands for natural matrix reference samples to support the analysis of geochemical materials, came with the advent of instrumental methods of analysis. The historical roots of these instrumental methods date from the mid-i88o s to the early 1900 s, but only later were the methods used in routine rock analysis. This use of instrumental methods of analysis generated a demand for rock reference samples, that could be used for calibration purposes. The earliest of them were analyzed by classical methods to determine major and minor oxides... 

The use of reference samples for method calibration and development/validation occurred hand-in-hand with the development of all modern instrumental methods of analysis. In fact, the two developments are intimately linked with one another. As already noted, G-i and W-i (Fairbaim et al. 1951 Stevens i960) illustrate first instance of reference samples specifically developed for calibration purposes. Following that, the use of BCR-i as a reference sample throughout the lunar program (Science 1970) is a prime illustration of the quality assurance and method validation applications in large-scale inter-laboratory measurement programs. 

Alternatively, fundamental parameter methods (FPM) may be used to simulate analytical calibrations for homogeneous materials. From a theoretical point of view, there is a wide choice of equivalent fundamental algorithms for converting intensities to concentrations in quantitative XRF analysis. The fundamental parameters approach was originally proposed by Criss and Birks [239]. A number of assumptions underlie the application of theoretical methods, namely that the specimens be thick, flat and homogeneous, and that, for calibration purposes, the concentrations of all the elements in the reference material be known (having been determined by alternative methods). The classical formalism proposed by Criss and Birks [239] is equivalent to the fundamental influence coefficient formalisms (see ref. [232]). In contrast to empirical influence coefficient methods, in which the experimental intensities from reference materials are used to compute the values of the coefficients, the fundamental influence coefficient approach calculates... 

Most of our discussion so far has centered on the use of the two-point-difference method of computing an approximation to the true derivative, but since we have already brought up the Savitzky-Golay method, it is appropriate here to consider both ways of computing derivatives, when considering how they behave when used for quantitative calibration purposes. 

Experiments were conducted in a large (-26 m3) radon/thoron test facility (RTTF) designed for calibration purposes and simulation studies (Bigu, 1984). A number of different materials were exposed in the RTTF to a radon/radon progeny or thoron/thoron progeny atmosphere. Exposure of the materials was carried out under laboratory-controlled conditions of radiation level, aerosol concentration, air moisture content and temperature. The materials used were in the form of circular discs of the same thickness (-0.5 mm) and diameter (-25 mm), and they were placed at different locations on the walls of the RTTF at about 1.6 m above the floor. Other samples were placed on horizontal trays. Samples (discs) of different materials were arranged in sets of 3 to 4 they were placed very close to one another to ensure exposure under identical conditions. Exposure time was at least 24 hours to ensure surface activity equilibrium, or near equilibrium, conditions. 

The realization of a CVGT with a high level of accuracy requires complex techniques and skill. It is mostly used by national laboratories for calibration purposes. For a detailed description of CVGT, see e.g. ref. [18]. 

Note (4) is very important as it highlights the fact that the reference material used for the method validation cannot be used again when the method is in routine use for calibration purposes. The same type of material can be used, but it needs to come from a different supplier. The same material cannot be used for calibration purposes and then as a quality control material. 

Table 3.4 lists some solutions and their conductivities that can be used for calibration purposes. 

Total pressure, required for detailed interpretation of the mass spectra, is determined with an ionization gauge (S). The gas inlet system (A, B, C) is used for calibration purposes. The relation between measured total pressure and the ion current of an injected specific gas permits calibration of the mass spectrometer in absolute partial pressure units or amps/torr. 

The sensor can either be mounted in a DIE28 package (dual-inline package with 28 pins) for testing and calibration purposes or in a TO-package (Fig. 6.15), which is... 

Experimental tilt angles have usually an accuracy of at best 3°, leading to an error of about 0.1 A in cell axes. The calculated third cell axis will show a higher deviation. If possible an internal standard should be used for calibration purposes but a higher accuracy will be obtained with a Pawley fit (e.g. fit forP CuPc in Fig. 6) from x-ray powder diffraction data [11]. Especially for packing energy minimization used for simulation methods it is essential to determine the cell parameters as precise as possible. In the case of polymorphism, it is essential to use x-ray powder diffraction to ensure that bulk and investigated nano crystals represent the same modifications. 

In this book, standard is used only in the sense of written standard and the term measurement standard or etalon (in French etalon )(see slide 36) is used to describe chemical or physical standards used for calibration purposes such as chemicals of established purity and their corresponding solutions of known concentration, UV filter, weights, etc. They are also called reference materials. 

And also as chemical or physical measurement standard, which is used for calibration purposes... 

In the past the McLeod vacuum gauge was also used for calibration purposes. With a precision-made McLeod and carefully executed measurements, taking into account all possible sources of error, pressures down to 10" mbar can be measured with considerable accuracy by means of such an instrument. 

Determining Calibration Curves frcm Polydisperse Samples. In conventional SEC interpretation, narrow molecular weight distribution standards are needed for calibration purposes. Nonlinear regression has enabled polydisperse scimples to be used. A variety of methods... 

We also performed extensive DFT studies on both the full target system and the model for calibration purposes. For details of one-electron basis sets used please consult Ref. (55). We used the B3LYP functional but found the ground-state potential energy surface to be relatively insensitive to the chosen functional (note though that this does not mean that DFT gives the correct surfaces, as important nondynamical correlation effects are... 

The PTS consists of two basic units, the chest pack (worn near the breathing zone), and the belt pack. The dosimeter controls the operation of the chest pack and stores the acquired sampling data. The LC display provides instantaneous update of the gas concentration being measured for observation or calibration purposes. 

Samples of this material as well as others investigated are now available for calibration purposes as gas adsorption standards. Details may be found in the reference cited for the data of Table 9.2. 

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